Viscosity measurements are carried out with complex machines that required constant calibration and long wait times. Changes in oil viscosity in vehicles operated in extreme conditions result in major breakdowns and repairs. Preventive maintenance schedules may not be enough to prevent these breakdowns. As such in-field viscosity monitoring is needed.
Current MEMS based viscosity sensors utilize changes in resonant frequencies of cantilever beams to correlate viscosity changes. These devices are considered vibration viscometers in which the damping of an oscillating electromechanical resonator immersed in the test liquid is measured. Complex actuation and sensing methods, which are usually non-CMOS compatible, make these devices quite challenging to fabricate and integrate.
Some of these prior complex actuation and sensing devices utilize an electromagnetic driven cantilever beam or plate which requires the use of a strong external magnet and an optical readout method which is not easily integrated. Others prior devices use ultrasonic piezoelectric actuation of a very long microprobe which raises material reliability questions. The use of a piezoelectric membrane with an optical read which improves the reliability, although not the CMOS compatibility also has been suggested.